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Feild, TS and Brodribb, TJ and Iglesias, A and Chatelet, DS and Baresch, A and Upchurch, GR and Gomez, B and Mohr, BAR and Coiffard, C and Kvacek, J and Jaramillo, C, Fossil evidence for Cretaceous escalation in angiosperm leaf vein evolution, National Academy of Sciences of The United States of America. Proceedings, 180, (20) pp. 8363-8366. ISSN 0027-8424 (2011) [Refereed Article]

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Abstract

The flowering plants that dominate modern vegetation possess
leaf gas exchange potentials that far exceed those of all other
living or extinct plants. The great divide in maximal ability to
exchange CO2 for water between leaves of nonangiosperms and
angiosperms forms the mechanistic foundation for speculation
about how angiosperms drove sweeping ecological and biogeochemical
change during the Cretaceous. However, there is no
empirical evidence that angiosperms evolved highly photosynthetically
active leaves during the Cretaceous. Using vein density
(DV) measurements of fossil angiosperm leaves, we show that
the leaf hydraulic capacities of angiosperms escalated severalfold
during the Cretaceous. During the first 30 million years of
angiosperm leaf evolution, angiosperm leaves exhibited uniformly
low vein DV that overlapped the DV range of dominant
Early Cretaceous ferns and gymnosperms. Fossil angiosperm vein
densities reveal a subsequent biphasic increase in DV. During the
first mid-Cretaceous surge, angiosperm DV first surpassed the
upper bound of DV limits for nonangiosperms. However, the upper
limits of DV typical of modern megathermal rainforest trees
first appear during a second wave of increased DV during the
Cretaceous-Tertiary transition. Thus, our findings provide fossil
evidence for the hypothesis that significant ecosystem change
brought about by angiosperms lagged behind the Early Cretaceous
taxonomic diversification of angiosperms.